Copenhagen is a play about quantum mechanics. At least, it is a play about the way one aspect of quantum mechanics, called "quantum indeterminacy," mirrors our understanding of history. In particular, it's about our understanding of one weird night in 1941 when Nazi scientist Werner Heisenberg visited his old friend, Niels Bohr, to talk about the Nazi plan to build a nuclear weapon. To mount it convincingly, Lewis had to understand a lot about the trickiest aspects of modern science, and he had to conceive of a way to get the point across to audiences who might understand none of it. His production communicated with remarkable cohesion on every level — from the blocking to the acting to the program to the lighting — and became a strange and frightening masterpiece.